Multimode Output Power Research Articles

Nanosecond pulsed single longitudinal mode diamond Raman laser in the 1.6 µm spectral region.

We demonstrate the first nanosecond pulsed single longitudinal mode (SLM) intracavity-pumped diamond Raman laser, to the best of our knowledge. The eye-safe coherent source at 1634 nm, which was converted from the actively Q-switched 1342 nm Nd:YVO4 laser, yielded 4.35 W of multimode average output power with a pulse duration of 6 ns and peak power of 29 kW. By exploiting the spatial hole burning free gain mechanism in the Raman media, stable SLM operation was observed at low output power (0.46 W) for the free-running case. Furthermore, by incorporating an etalon in the fundamental standing-wave cavity, the spectral linewidth of the fundamental field was suppressed substantially below the diamond Raman gain linewidth and slightly less than the free spectral range of the mm-scale Raman resonator. Thereby, a much higher SLM output power of 1.63 W was obtained with a pulse duration of ∼9 ns and a spectral linewidth of ∼77 MHz.

30-GHz Bandwidth With Directly Current-Modulated 980-nm Oxide-Aperture VCSELs

Directly current-modulated 980-nm vertical-cavity surface-emitting lasers (VCSELs) with oxide-aperture-diameters of $1.5~\mu \text{m}$ exhibit a small-signal −3 dB modulation bandwidth of 31 GHz and a single-mode light-output-power of 3 mW with a side-mode-suppression-ratio (SMSR) of 49 dB at 25 °C at a forward bias current of 3 mA. At 85 °C, the maximum bandwidth is about 25 GHz, the peak power is about 2 mW, and the SMSR remains 49 dB. The bandwidth for a 5.5- $\mu \text{m}$ oxide-aperture-diameter VCSEL reaches 26 and 21 GHz at 25 °C and 85 °C, respectively, with corresponding maximum multi-mode optical output power of about 10 and 6 mW.

Astigmatism-free high-brightness 1060 nm edge-emitting lasers with narrow circular beam profile.

1060 nm high-brightness vertical broad-area edge-emitting lasers providing anastigmatic high optical power into a narrow circular beam profile are demonstrated. Ridge-waveguide (RW) lasers yield record 2.2 W single-transverse mode power in the 1060-nm wavelength range under continuous-wave (cw) operation at room temperature with excellent beam quality factor M2 ≤ 2. Independent of operating current the astigmatism is only 2.5 µm. 3 mm long broad-area (BA) lasers produce a θvert as narrow as 9° full width at half maximum, which agrees well with our simulation results, being insensitive to drive current. 5 mm long BA lasers deliver highest ever reported cw 12 W multimode output power among lasers showing θvert <10° in the 1060-nm wavelength range. The emitted laser beams from both RW and BA lasers show a perfect circular shape with ≤10° divergence angle at record 2.1 W and 4.2 W cw-mode output power, respectively.

Single longitudinal mode diamond Raman laser in the eye-safe spectral region for water vapor detection.

We report a narrowband and tunable diamond Raman laser generating eye-safe radiation suitable for water vapor detection. Frequency conversion of a tunable pump laser operating from 1063 to 1066 nm to the second order Stokes component in an external standing-wave cavity yielded 7 W of multimode output power in the wavelength range from 1483 to 1488 nm at a conversion efficiency of 21%. Stable single longitudinal mode operation was achieved over the whole tuning range at low power (0.1 W), whereas incorporation of a volume Bragg grating as an output coupler enabled much higher stable power to be attained (0.5 W). A frequency stability of 40 MHz was obtained over a minute without active cavity stabilization. It was found that mode stability is aided via seeding of the second Stokes by four-wave mixing, which leads to a doubling of the mode-hopping interval. The laser was employed for the detection of water vapor in ambient air, demonstrating its potential for remote sensing applications.

Resonantly pumped monolithic nonplanar Ho:YAG ring laser with high-power single-frequency laser output at 2122 nm

We demonstrated a stable single-frequency laser operating at 2122 nm from a monolithic nonplanar Ho:YAG ring oscillator (NPRO). The Ho:YAG NPRO was resonantly pumped by a 1907 nm Tm:YLF laser built up by ourselves. The maximum multimode output power from the Ho:YAG NPRO was 9.66 W and the slope efficiency was 71.7%. With accurate adjustment of the pump position to make the laser oscillate in single frequency condition, an output power of 8.0 W was obtained with a slope efficiency of 61.4% and an optical-optical efficiency of 50.0%. The power stability of the Ho:YAG NPRO laser was 0.29% at maximum single frequency output power. The beam quality M(2) factors were measured to be less than 1.1 in x- and y- directions.

Resonantly (in-band) cladding-pumped Yb-free Er-doped fibre laser with record efficiency

Power scaling potential with record high efficiency for a resonantly (in-band) cladding-pumped Yb-free Er-doped eye-safe fibre laser utilising the fibre with non-clustering composition and increased cladding pump absorption is domonstrated. While pumping at 1532.5 nm by power-combined fibre-coupled spectrally-narrowed InGaAsP/InP diode laser modules, ∼47 W of continuous-wave multimode output power at ∼1590 nm with optical-to-optical efficiency over 77% were achieved. To the best of the authors' knowledge, this is the highest efficiency ever obtained from a cladding-pumped Yb-free Er-doped fibre laser.

High repetition rate dual-rod acousto-optics Q-switched composite Nd:YVO4 laser

We demonstrate the high-repetition rate acousto-optic Q-switching of a dual-rod Nd:YVO4 laser. Two thermally bonded composite YVO4-Nd:YVO4-YVO4 rod crystals were used as the gain medium to reduce the serious thermal effect. The pump mode and its influence on the laser mode were analyzed, and the effective pump radius was controlled by tuning the spectrum of laser diodes with adjustment on the temperature of laser diodes. Three different configurations of cavity optics were designed and the output performance using these cavities was investigated. In Q-switching operation, 73.2 W TEM00 mode average power at 650 kHz was obtained. The stable Q-switching range was from 80 kHz to 650 kHz with the pulse duration increasing from 17.5 ns to 80 ns. In CW operation, 78 W TEM00 mode and 93 W multi-mode output power was achieved with different cavity designs, corresponding to the optical-optical efficiency of 46.5% and 52.2% respectively.

Study on single-transverse mode output of high-power flat He–Ne laser

The multimode output power of He-Ne lasers with a flat discharge tube can be enhanced by increasing the transverse size of the discharge tube. By using an N-type fold optical resonator, the high-power flat He-Ne laser tube can give the output in the lower-order mode. Inserting a limiting-mode circular-hole diaphragm into the N-type fold optical resonator, the lower-order modes are suppressed gradually with the reduction in its aperture. The high-power flat He-Ne laser tube of 1.4 m discharge length can achieve above 80 mW of the single-transverse mode output power using an N-type fold optical resonator with a limiting-mode circular-hole diaphragm of 4 mm aperture. Its output characteristics and laser mode patterns are investigated experimentally. The experimental method is introduced and its results are discussed briefly in this paper.

Compact TEM00 grazing-incidence Nd:GdVO4 laser using a folded cavity

A compact diode-side-pumped Nd:GdVO4 laser system using a folded cavity and grazing-incidence configuration is presented. The highest multimode output power obtained was 21.8 W at 36 W of effective diode pump power. Highest optical-to-optical conversion efficiency of 61.5% was achieved at 33 W of effective diode pump power with 20.3 W of multimode output power. For single-mode TEM00 operation, an intracavity telescope was adopted for mode matching in the horizontal direction. Because of the folded cavity and the intracavity telescope, this laser head was the most compact to our knowledge of the TEM00 grazing-incidence laser geometry. At last, an output power of 15 W was produced at 36 W of effective diode pump power. The stable Q-switching operation was also obtained.

High-power scaling (&gt;100 W) of a diode-pumped TEM/sub 00/ Nd:GdVO/sub 4/ laser system

We present results of an investigation to scale a diode-pumped A Nd:GdVO/sub 4/ laser system to high powers (>100 W) using a bounce amplifier configuration. A Nd:GdVO/sub 4/ laser oscillator with a bounce amplifier geometry, pumped by a single 40-W diode bar, gave 24 W of multimode output power (60% optical efficiency), and 20 W of TEM/sub 00/ output with M/sup 2/<1.05. Power scaling of the oscillator system with pumping by multiplexing two (nominally) 40-W diode bars gave 50.1 W of multimode output at 83-W diode pumping, 40 W of predominantly TEM/sub 00/ output from 81-W of diode pumping, and 34 W TEM/sub 00/ output (M/sup 2//sub x/=1.05,M/sup 2//sub y/=1.1) with an external slit spatial filter. Higher power scaling is achieved by using a master-oscillator power-amplifier (MOPA) configuration with the double-diode-pumped oscillator and a bounce amplifier pumped by a 3-bar diode stack. A multimode MOPA output of 100 W is achieved by single pass amplification with 145-W amplifier diode pumping and 104-W TEM/sub 00/ mode using a double bounce amplifier configuration with 180-W amplifier diode pumping.

Molecular-beam-epitaxy growth of high-quality InGaAsN∕GaAs quantum well lasers emitting at 1.3μm

Molecular-beam-epitaxy growth of high structural and optical-quality InGaAsN∕GaAs quantum wells (QW) has been investigated. The material quality can be improved significantly by using low-temperature growth to suppress the phase separation. High-performance ridge-waveguide InGaAsN∕GaAs single QW lasers emitting at 1.3μm have been demonstrated. Infinite-cavity-length threshold-current density of 400A∕cm2, internal quantum efficiency of 96%, and a slope efficiency of 0.67W∕A for a cavity length L=1mm were obtained. A TO46 packaging laser shows single lateral-mode kink-free output power of more than 200mW with a maximum total wallplug efficiency of 29% at room temperature under continuous wave (cw) operation. Moreover, 1.3μm InGaAsN∕GaAs QW vertical-cavity surface-emitting lasers with a threshold current density lower than 2KA∕cm2 at room temperature have been achieved. We obtained multimode cw output power and slope efficiency in excess of 1mW and 0.15W∕A, respectively.

High-performance 1.3 µm InGaAs vertical cavity surface emitting lasers

A report is presented on high-performance InGaAs/GaAs double quantum well vertical cavity surface emitting lasers (VCSELs) with record long emission wavelengths up to 1300 nm. Due to a large gain-cavity detuning these VCSELs show excellent temperature performance with very stable threshold current and output power characteristics. For 1.27 µm singlemode devices the threshold current is found to decrease from 2 to 1 mA between 10 and 90°C, while the peak output power only drops from 1 to 0.6 mW. Large-area 1300 nm VCSELs show multimode output power close to 3 mW.

High-average-power Nd:YAG planar waveguide laser that is face pumped by 10 laser diode bars

A planar waveguide Nd:YAG laser is pumped with 430 W of power from 10 laser diode bars to produce a multimode output power of 150 W at an optical efficiency of 35%. Use of a hybrid resonator of the positive-branch confocal unstable type for the lateral axis and of one of the near-case I waveguide type for the transverse axis increased the laser brightness by a factor of ~26 with only 12% less power than in the multimode case.

Continuous-wave Nd:YVO 4 grazing-incidence laser with 22.5 W output power and 64% conversion efficiency

Very high-efficiency and high-power operation of a continuous-wave Nd:YVO 4 laser is demonstrated using a grazing-incidence geometry with diode side pumping. With 35 W diode bar pumping, multimode output power of 22.5 W (optical-to-optical conversion efficiency of 64%) with slope efficiency of 72%, and single mode output power of 13.8 W (conversion efficiency of 40%) is produced at wavelength 1064 nm. Small-signal gain and thermal lensing in the amplifier are investigated to explain the very high efficiency and spatial characteristics of the laser system.

Yb:YAG and Nd:YAG edge-pumped slab lasers

Experimental demonstrations of two edge-pumped zigzag slab lasers are presented. The Nd:YAG slab laser generated 127 W of multimode output power with 300W of pump power. Preliminary results with a Yb:YAG slab produced 46 W of output power with 315W of pump power. The edge-pumped slab design permits symmetric conduction cooling and efficient pump absorption and accepts large-numerical-aperture pump sources.

Collision broadening and quantum noise in a very large laser gyroscope

The single mode and the multimode output power are studied as a function of the input power and the partial pressure in a very large (perimeter=14 m) He:Ne ring laser gyroscope and in a linear He:Ne laser (length=1.6 m). The effects of collision broadening on the single mode output power are discussed. For a sufficiently high He:Ne pressure, the gain of adjacent longitudinal modes is depleted and multimode emission is suppressed and hence the single mode output power of the ring laser is increased. The quantum noise and the long term drifts in the Earth rotation induced Sagnac frequency ( ν S=288.5 Hz) are investigated. The demonstrated advantages of operating a laser gyroscope at a large He:Ne pressure are: reduction in quantum noise and the freedom to choose the input power within a large range.

Efficient diffusive reflector-type diode side-pumped Nd:YAG rod laser with an optical slope efficiency of 55%

We fabricated a compact diode side-pumped Nd:YAG laser with a diffusive reflector, in which the diode laser power is transferred directly into the threefold symmetric diffusive cavity through long narrow slits. With a 7.5% output coupler in a linear resonator, we obtained 62.4-W multimode output power with an optical slope efficiency of 53.4% at a diode power of 182 W, which corresponds to an optical-to-optical efficiency of 34.3%. The optical slope efficiency increased to 55.5% when we used an 11% output coupler. From the leakage power analysis method, the pumping efficiency was measured to be approximately 82%. We discuss the thermal lens and the slope efficiency with respect to absorbed power that is derived from the measured pumping efficiency.

Dependence of gain and output power on cathode to anode area ratio in a segmented hollow-cathode Cu-II 781 nm laser

The characteristics of a segmented hollow-cathode He - 781 nm laser are modified by varying the cathode to anode area ratio (C/A), in steps from 3.0 to 0.33, for a fixed bore diameter of 4 mm. The discharge voltage for a given current to pressure ratio, and consequently the small-signal gain and multimode output power for a given current, are significantly increased when C/A is reduced. For a given gain in excess of 20% , the input power decreases slightly as C/A is reduced. However, for a given multimode output power, the input power is almost independent of C/A (0.33 to 2.0). For a gain of 60% the current density decreases from 450 to 340 mA when the area ratio is reduced from 3 to 0.5.

A novel approach for compensation of birefringence in cylindrical Nd: YAG rods

A new concept for compensation of birefringence in solid-state rod lasers is presented. The basic idea of our approach is the simultaneous use of an in-cavity polarization rotator and an imaging optical system between the two passes through the laser rod. The theoretical analysis based on matrix optics shows that perfect compensation for the birefringence and bifocusing in laser rods is possible for a large pumping range. Experimental results with two Nd:YAG rods are also presented. The measured depolarization loss per transit for a test beam at 0.63 μm is less than 5% for pumping power up to 6kW per rod. This would allow efficient generation of high-power TEM00 mode and linearly polarized multimode output power from Nd:YAG oscillators in rod geometry.

High Efficient Diode-Side-Pumped Nd:YAG Laser by Total-Reflective Transfer and Diffusive Reflection.

We propose a novel high efficient diode-side-pumping configuration of a solid-state laser. The optical slope efficiency of 52.2% was proved in a continuous-wave mode, an efficiency which is, to our knowledge, the highest for diode-side-pumped Nd:YAG rod lasers. The electrical-to-optical slope efficiency was 30.3%. With a diode output power of 135.1W and an electrical input power of 327.3W into diode arrays, we obtained a multi-mode output power of 40.0W which corresponds to a total optical efficiency of 29.6% and a total electrical-to-optical efficiency of 12.2%.